The neurobehavioral effects of opiates are studied in adult and neonatal cats to define the role of specific brain areas (caudate nucleus and brain stem) in chronic and acute use and to establish the use of the cat as a model for the study of tolerance and consequences of perinatal addiction. Differences in response to single dose effects of morphine and endorphin and the effects of chronic morphine administration are assessed in intact and brain lesioned animals. The effects of caudate removal on morphine self-administration and of maternally administered morphine on the behavioral and neurological development of the kitten are also investigated.